A light-emitting diode (LED) has been used as a light source as result of improvement in output and light-emitting efficiency, and becoming popular. A lighting apparatus using an LED has been developed as a luminaire used indoor or outdoor. In such a luminaire, a plurality of light-emitting elements such as LEDS is directly mounted on a substrate, and each light-emitting element is sealed by being covered with a fluorescent layer as a sealing resin layer containing a fluorescent material.
In this case, a light-emitting element is densely mounted on a substrate to increase the amount of light for a luminaire. Heat is concentrated on a part of substrate where a light-emitting element is mounted. As a result, the temperature of a light-emitting element is excessively increased. As the temperature of a light-emitting element such as an LED is increased, an output of light is decreased, and an expected lifetime is reduced. Therefore, for a luminaire using a solid light-emitting element such as a light-emitting diode (LED) or electroluminescence (EL) as a light source, it is necessary to prevent a temperature increase of a light-emitting element for increasing an expected lifetime and improving a performance such as brightness efficiency. To prevent an excessive temperature increase of a light-emitting element, various heat radiation means has been adopted. For example, a radiating structure with excellent heat conductivity is bonded to a substrate.
There is a luminaire, in which a plurality of surface-mount LED packages is mounted on a substrate. Comparing with direct mounting of a light-emitting element such as an LED on a substrate, an LED package is large as a single element, and has a large output of light. Therefore, a mounting density of LED package is low when input power per area of mounting part on a substrate is the same. In other words, the number of light-emitting points per unit area is small.
Therefore, an LED package is easy to be identified as a spotted light source during emission of light, and easy to cause uneven brightness.
When a light-emitting element is densely and directly mounted on a substrate as described above, heat is concentrated in a part of substrate where a light-emitting element is mounted, and the temperature of a light-emitting element is excessively increased. If a surface-mount LED package with the same input power is mounted on a substrate instead of a light-emitting element, it easily causes uneven brightness.